WO2012/140201 (incorporated herein by reference) describes a bridge plug tool of the general type to which this invention applies. Releasing such tools from position in a well typically comprises two operations: equalization, in which the fluid pressure in the well above and below the tool is equalized, and release in which the setting force applied to expand anchor and packer members is released, allowing the anchors and packer to contract to release the tool from the well.
The tool described in WO2012/140201 comprises two mechanisms for each operation. The primary equalization and release mechanisms are provided for normal use in which the operations are carried out under optimal control and the tool is easily reset for further use by returning parts of the tool to initial positions and replacement of shear screws, seals, etc. The secondary equalization and release mechanisms are provided in case the primary mechanisms fail and the tool would otherwise remain stuck in the well. However, operation of the secondary mechanisms is more severe and requires significant reconditioning of the tool before it can be used again.
One or both of the secondary equalization and release mechanisms described in WO2012/140201 requires application of torque and a rotary, unscrewing, motion. Such force can be difficult to apply downhole.
This invention aims, inter alia, to provide secondary equalization and release mechanisms that can be operated using axial (push or pull) forces, that can be easily generated downhole